This invention relates to an image reproduction process and, more particularly, to a relief printing process using low-relief printing forms in conjunction with a transferable, non-liquid marking material.
The spirit duplication process is frequently used when it is desired to produce a low or intermediate volume of copies at low cost. This process requires preparation of a master which carries a laterally reversed, soluble-dye image of the information to be reproduced. One common method of preparing such a master copy is to place the marking side of a sheet of soluble-dye-bearing paper such as carbon paper in contact with a first side of the master sheet so that when information is written or typed on the other side of the sheet, the dye is transferred to the first side of the master sheet. Another method of preparing such a master copy is to expose a light sensitive hydrophilic organic colloid layer capable of being differentially tanned or hardened under influence of light, such as an unhardened gelatino-silver halide emulsion layer to an imagewise pattern of light. Subsequent to the imagewise photoexposure, the colloid matrix sheet is contacted while moist with a clean absorbent sheet of paper to transfer a thin stratum of the unexposed tacky areas of the light sensitive element to the paper which forms a relief image after the sheets have been separated. Shortly thereafter, while the relief image is still moist, the paper is squeegeed against a spirit duplicating master sheet of a type well known in the art carrying a soluble dye so that the dye adheres to the relief image when the sheets are separated.
The dyes, such as carbon ink, used in the spirit reproduction process are soluble in various organic solvents such as alcohol, acetone and the like. When it is desired to make reproductions, a receiver sheet of plain paper is slightly moistened with such a solvent and pressed into contact with the master sheet whereby a small amount of the dye is transferred to the receiver sheet. While advantageous from a cost standpoint, spirit reproduction processes have the disadvantages of requiring solvent treatment and producing prints exhibiting relatively low image definition and a high amount of background smudging.
Another low volume copying process disclosed in Canadian Pat. No. 817,079 forms an electrostatic image on a support material and then develops such image with a hard, comparatively coarse, granular material (average grain diameter between 50 and 250 microns) to form a relief image. The developed relief image, held in place by electrostatic attraction, is overlaid with one or more sets of carbon paper and associated receiver paper and printed using a mechanical pressure printing apparatus. One to five dry copies can be reproduced by this process, however, the image sharpness of the copies is relatively low as a result of the lateral movement of the toner particles during the printing operation and the pressure of the intervening carbon sheets. Another disadvantage of this process is that the relief image cannot be reused because it is not permanently fixed to the support.